I tried to do some research on what cause the
different mass extinctions. I know there are
different theories but I only found concrete info
on the 65 million years ago extinction. What was
the cause of the 245 million years ago mass
extinction? Thanks.

Question Date: 2003-04-08

Answer 1:

The extinction that occurred 245 million years ago
was in the late Permian period. The causes are
thought to be fluctuations in sea-level, a change
in the salinity of the ocean, and volcanic
activity.

As you've probably noticed while doing your
research, there are many hypotheses about why mass
extinctions occur.

Just a side note: All the
divisions of the geologic time scale are based on
extinction events determined by the disappearance
of certain fossils from rocks of a given age. At
the boundary between the Permian and Triassic (245
million years ago), something happened that caused
the extinction
of about 95% of all marine invertebrates and 70%
of terrestrial vertebrates. Here are two of the
most widely accepted hypotheses for what
happened:

1. Formation of the supercontinent
Pangea:
The joining of multiple continents
into one continent would decrease the amount of
shallow marine shelf environment available as
habitat. Most marine organisms live in shallow
environments. In addition, the center of the
supercontinent was probably dry and hot, providing
miserable habitat for terrestrial animals.

2. Climate change and carbon dioxide
buildup:
This hypothesis is also related to Pangaea. The
idea is that the formation of Pangea drastically
changed ocean circulation patterns so that
circulation became slow and the oceans were poorly
mixed (i.e., deep water stays in the depths
instead of upwelling). Photosynthetic marine
organisms like phytoplankton sink to the bottom of
the ocean when they die, and aerobic bacteria at
the bottom of the ocean consume them, producing
carbon dioxide. In the late Permian, this carbon
dioxide was stuck on the bottom of the ocean
instead of being driven to the surface and
released to the atmosphere. The atmosphere,
therefore, became depleted in carbon dioxide.

Carbon dioxide is a greenhouse gas that helps keep
the atmosphere warm, and when it was depleted, the
climate cooled. Climatic cooling led to
glaciation, which caused the ocean surface
temperatures to decrease. This led to sinking of
ocean surface water because the colder surface
water was denser than the underlying, warmer
water. As the oceans began to mix, all that
carbon dioxide trapped at the bottom was released
into the atmosphere (think of a big carbon dioxide
belch). Oxygen-breathing creatures on land and in
the sea were suffocated by the huge amount of
carbon dioxide released.